The present invention generally relates to display and graphic systems and methods and, more particularly, to such systems and methods which can provide visual output for computers.
Today's personal computer market, like so many other successful areas of technology, is a product of evolution and not revolution. IBM compatible personal computers (PCs) have been designed such that software purchased a decade ago will run unmodified on the latest release of computer hardware. Microsoft's DOS operating system has evolved without requiring rewriting of applications purchased or written at the beginning of the PC's history. Likewise, Microsoft's Windows operating system, even though significantly more advanced and functioning on a completely different user interface than DOS, still provides convenient access to the older DOS environment. However, the price that must be paid to maintain this backward compatibility comes in terms of additional software complexity and higher hardware cost.
There has been a long history of evolution of the display controller and display monitors used in IBM compatible PCs. The first and most basic of the display modes used in these devices is known as character mode. A standard originally defined by the MC6845 CRT controller, character mode circuits create an array of fixed sized and fixed font text similar to the text seen in alpha-numeric terminals in the late '70s. The familiar C: prompt is most commonly seen in character mode. In fact most DOS commands and the boot sequence of the PC use character mode. The video sent to the monitor to display text in character mode is a 720 pixels by 400 scan line image. All PCs and display monitors today support this low resolution character mode.
While the requirements for character mode have been constant throughout the history of the PC, bit mapped graphics requirements have evolved continuously. PC bit mapped graphics began with the original Color Graphics Adapter (CGA) and Hercules graphics standards which evolved into the Enhanced Graphics Adapter (EGA) standard and then the Video Graphics Adapter (VGA) standard. There were no significant graphics software applications programming interfaces (APIS) to buffer the software applications from the physical hardware interface in the DOS environment. Thus, every piece of applications software required a different applications device driver for each of the different graphics resolutions and color capability which has evolved.
Today, the PC industry generally accepts the VGA 640.times.480 pixel resolution graphics mode as the minimum acceptable resolution for running the more sophisticated Microsoft Windows applications. Since Windows does use a standardized applications programming interface (API) for graphics, higher resolutions such as 800.times.600, 1024.times.768, and 1280.times.1024 pixels can be used by simply installing the appropriate Windows graphics device driver. This allows applications software designed for Windows to remain totally independent of the graphics hardware.
If one could simply discard all of the old DOS applications software, the old DOS graphics compatibility hardware problems could simply be ignored in favor of the well structured Windows environment. Since many computer users fear hardware obsolescence and base their purchasing decisions on products having a history of supporting legacies, this has never been allowed to happen. Although the cost of the PC graphics controller has not been adversely affected by this backward compatibility feature, the modem PC display monitor has not been so fortunate.
The CRT display monitor evolution has been much more complicated than that of the graphics industry in general. The PC standard has required the monitor manufacturers to design display monitors which can handle every resolution below their maximum nominal performance. For example, a VGA color monitor in 1989 was required to support not only the 640.times.480 VGA resolution, but also the EGA 640.times.350, CGA 320.times.200, and 720.times.400 character mode resolutions. These multisync monitors have been required to adapt to nearly any video signal which any graphic controller outputs and produce a quality picture.
Today, the best multisync monitors can adapt to resolutions up to 1600.times.1200 pixels while still providing adequate image quality in character mode. Microprocessor-based circuitry within the monitor provides the necessary adaptive adjustments and controls, largely sheltering the user from having to make manual adjustments to the monitor as it switches resolutions. This added circuitry is very expensive, particularly in the higher end multisync monitors, when compared to the single frequency monitors used in the workstation markets.
It is important to note that even today, Microsoft's most advanced operating system "WINDOWS NT", requires the display system to begin in character mode while the machine boots and runs its diagnostic software. In today's world the latest DOS applications have settled on the VGA 640.times.480 resolution as a standard, while the Windows environment generally runs in the highest native resolution supported by the monitor, which can be, for example, from 640.times.480 to 1280.times.1024. Thus, the aforementioned complexity problem which has increased the cost of monitors in the PC world shows no signs of abating.
The workstation market and the Apple "MACINTOSH" market have not been plagued by the same problems as the PC market. These markets have not required the use of multisync monitors because of their generally short legacies and well structured graphics device drivers, allowing the applications designed for these systems to be free of any hardware specifics. Typical fixed resolution monitors used by workstation vendors have included, for example, resolutions of: 1024.times.768, 1152.times.900, 1184.times.884, 1280.times.960 and 1280.times.1024. These monitors have operated at a fixed screen refresh rate of between 60 and 76 Hz.
Within the context of PC graphics controllers, no low cost means currently exists for real time conversion of low resolution digital video generated by a PC, and synthesizing this video for a fixed scan frequency higher resolution monitor. U.S. Pat. No. 4,866,520 to Nomura et al discloses a system for adapting television signals to CRT displays of computer monitors. Since this patent relates to television signal transformation, however, it fails to recognize the need for, and problems associated with, transforming a plurality of different low resolution computer graphic data modes into a higher resolution video signal. For example, Nomura et al. fails to provide interpolation based on an actual area of coverage or average energy intensity of a data line but instead relies on predetermined selection patterns.
Similarly, U.S. Pat. No. 4,935,731 to Takebe et al. discloses an image display system, and, in particular, a liquid crystal display panel, which transforms signals, but provides an interpolation method using two modulo counters for selecting one of two signals and fails to treat the problems associated with changing horizontal pixel spacing.